1. Field of the Invention
The present invention relates to a microphone capsule support which is mounted in the microphone housing and serves as an elastic suspension of the microphone capsule which is mounted in the microphone.
2. Description of the Related Art
Independently of the manner of operation of the microphone capsule, hereinafter called capsule in short, it is necessary in all microphones to mechanically connect the capsule to the microphone housing, on the one hand, and, on the other hand, to acoustically insulate and separate the capsule from the gripping noises. For solving these two opposite objects, so-called elastic rubber bearings are known in the art. These rubber bearings are collar-shaped or spider-shaped structures made of an elastic rubber or a rubber-like material into which the capsule is embedded and which is glued or clamped in the interior of the microphone housing or is permanently or separably connected in some other manner to the microphone housing
Since all microphone capsules are sound pressure transducers, two basic problems have to be confronted: the microphone capsule is not capable of distinguishing between useful sound and undesirable shaking movements of the microphone capsule. Both types of excitation have the same effect: the diaphragm of the microphone capsule is moved which consequently results in an electrical signal at the microphone output. It is apparent that an electrical signal which is generated by shaking the microphone is not desirable. Therefore, microphone manufacturers attempt to use structural measures for keeping the shaking or gripping noises as small as possible.
In the mechanical system, the microphone capsule and the elastic suspension or elastic support can be considered a mass/spring system. In the mechanical analysis of such systems, one arrives at the differential equations whose solutions constitute a complete description of the mechanical system. Since, considered formally, the above-mentioned differential equation of the mechanical resonant circuit (mass/spring damping) completely corresponds to a differential equation of the electrical resonant circuit (inductivity/capacity resistance), it is possible to carry out an analysis in the electrical domain by means of analogy computations.
In these computations, the mass m corresponds to the inductivity L, the spring c corresponds to the capacity C, and the damping k corresponds to the ohmic resistance R.
Since mechanical tools are easier to use for electrical engineering (computation with complex impedances), it is possible in this manner to more quickly obtain the result than would be the case when solving the mechanical basic equations. Subsequently, the results from the electrical domain are transformed into the mechanical domain, and the movements of the microphone are thus completely described with respect to time as well as with respect to frequency.
When answering the question as to how the mass/spring system should be adjusted so that the microphone reacts less sensitively to shaking or gripping noises, first the question concerning the limits of the transmission range of the microphone must be answered. Microphones are built for different purposes and, in dependence on this purpose, the lower and upper frequency limits are selected differently on a case by case basis. Generally, it can be stated that high-quality microphones have a wider frequency range, in the direction of lower frequencies as well as in the direction of higher frequencies, than is the case in microphones of lower quality. Since the excitation of the microphone capsule by shaking or gripping noises takes place in the low-frequency range, the lower frequency limit plays an important role for the behavior of a microphone in relation to the interference excitations transmitted by the microphone.
Expressed differently, if the frequency pattern of a microphone reaches to the lowest frequencies which are still perceptible by the human ear, its behavior relative to shaking or gripping noises will be much more sensitive than in a microphone whose lowest frequency limit still to be transmitted is adjusted at a higher level.
Consequently, it is possible to make a microphone less sensitive to shaking and gripping noises by adjusting its lower limit frequency at a higher level. However, microphone capsules and microphones adjusted in this manner lose some of their audio quality.
Some microphone manufacturers mount additional electrical filters in the microphone. These are so-called step sound filters which are switched on when the microphone is mounted on a stage microphone stand and interference noises, for example, step noises, must be expected from the stage floor. The electrical filter is adjusted in such a way that low frequencies are cut off electrically. Since an electrical filter can also not distinguish between useful and interference signals, when the step sound filter is switched on, useful sound is also unintentionally weakened i dependence on the frequency in accordance with the filter characteristic. As a result, a good microphone becomes a microphone of lower quality.
The tendency of development in the prior art is the following: it is being attempted not to limit the transmission range of the microphone capsule in the lower frequency range and, for this purpose, to adjust the elastic support of the microphone capsule in such a way that the mechanical resonant frequency of the system composed of capsule and support is adjusted at such a low level that it is outside of the frequency range to be transmitted. This is easily possible in a microphone with a lower frequency limit of 200 Hz; however, in microphones of higher quality with a lower frequency limit of 20 Hz, this is substantially more difficult.
As is generally known from the above-mentioned analysis of the differential equations, in the immediate vicinity of the mechanical resonant frequency of a mechanical resonant system amplitudes occur which are substantially greater than the amplitudes of the excitation signal. In order to reduce this undesirable amplitude increase, rubber or rubber-materials are used for the support, wherein these materials provide a high degree of internal damping. These materials convert the mechanical energy supplied from the outside by shaking the microphone housing into heat.
These materials used fulfill their purpose in non-problematic surroundings in a satisfactory manner; however, even if these materials are used, there are a number of problems: materials with high resiliency are adjusted with high damping by adding various chemical and mechanical additives. This has the consequence that the material has a high temperature dependency of its mechanical properties (strength, elasticity) and, thus, reacts strongly to different climatic conditions. Thus, the supports known in the art for high-quality microphones lose their elasticity almost completely already at temperatures of slightly above 0° C., and they become hard, which leads to a completely ineffective capsule support.
On the other hand, the rubber support becomes so soft already at temperatures around 40° C. that there is the danger that the capsule sags through as a result of its own mass to such an extent that it contacts the inner side of the microphone housing which also leads to a completely ineffective capsule support.
However, not only the unsatisfactory temperature stability of the rubber supports constitutes a serious problem in the use of the support; aging is another serious problem. Rubber is attacked by ultraviolet light to a significant extent and, due to the unavoidable loss (due to evaporation) of so-called softeners (chemical additives which have the purpose of softening the rubber), the rubber becomes brittle and breakable.